Rheology modifiers impart desirable rheological properties to coating formulations over a wide shear rate range. Many paints made with vinyl acetate-ethylene copolymer (VAE) based binders use cellulosic thickeners such as hydroxyethyl cellulose (HEC), hydroxymethylethyl cellulose (HMEC), and hydrophobically modified HEC (HMHEC) to achieve a desirable rheological profile. Cellulosic thickeners also impart heat age stability to such paints, resulting in stable viscosities after exposure to elevated temperature conditions.
Synthetic thickeners such as hydrophobically modified urethane polymers (HEUR) and hydrophobically modified alkali soluble emulsions (HASE) are also capable of thickening VAE based paints to achieve desirable rheological properties. HEUR rheology modifiers have the disadvantage of being too expensive for this class of paint formulations; moreover, matching the rheological performance of HEC thickeners with HEUR thickeners has proven to be a challenge, presumably because HECs thicken paints by way of a volume exclusion mechanism, whereas HEURs thicken paints via an associative thickening mechanism.
HASE thickeners are attractive low cost alternatives to HECs. For example, ACRYSOL™ DR-110 Rheology Modifier (A Trademark of The Dow Chemical Company or its Affiliates) was recently developed to replace HEC in acrylic based paint formulations. VAE paints thickened with DR-110 offer an attractive rheological profile compared to HEC thickened VAE paints; nevertheless, DR-110 thickened VAE based paints tend to be unstable and gel upon heat aging. It would therefore be desirable to find a low cost alternative to HECs to use as thickeners is VAE based paints that are heat age stable.